1. FIELD OF THE INVENTION
This application relates to power transmission chains and particularly to an improved rocker joint for such chains.
2. BACKGROUND DISCUSSION
Power transmission chains of the "silent" or inverted tooth variety usually comprise a plurality of sets of transversely aligned links which are interleaved with other sets of links. Each link has a body with a pair of spaced openings and the openings of one set of links are arranged and aligned with the openings of the next adjacent set of interleaved links. To join the interleaved sets of links, a pivot means is inserted into each group of aligned openings. As taught in the prior art, round pins and rocker joints have been used, the rocker joints comprising a pair of pins, or a pin and a rocker, each with a front face which contacts and rocks on the other. Each link of a silent chain, with the exception of guide links which do not mesh with sprocket teeth, has a body and a pair of depending toes separated by a crotch, each toe being defined by flanks which diverge toward the body. It is also conceivable to construct a chain with links similar to those of the American or British standard roller chain, but with interleaved links. The ultimate use of a chain dictates its construction.
Rocker joints for chains are well known in the prior art, as for example, U.S. Pat. Nos. 1,534,494; 3,540,302; 3,747,776; 4,010,656 and 4,507,106.
U.S. Pat. No. 1,534,494 teaches a power transmission chain in which the links have generally circular openings, each with a pair of inwardly directed tabs defining a pair of arcs of different lengths, and each set of openings receiving a pair of pins having generally curved backs and ogee fronts which rock on one another as the chain articulates.
U.S. Pat. No. 3,540,302 shows a chain having a rocker joint comprising a pair of like members, each member having a rocking surface in rocking contact with the other. The rocking surface of each is defined by a first radius, while the remainder of the member is defined by a surface of a second and smaller radius. Both surfaces are convex. The openings in the links for receiving each member are generally rectangular, and each joint member has spaced notches in which the link members seat to transmit the working load to the assembly.
U.S. Pat. No. 3,742,776 discloses a silent chain with a rocker joint comprising a pair of like members, each having a rocking surface engaging the other. The rocking surfaces are defined by a first radius, while the back surfaces of each member are defined by a second and smaller radius. The rocking and back surfaces are joined by planar or straight surfaces. The links of the chain have openings formed of inner and outer circular segments joined by wall segments which define straight chords of a circle. The members of the rocker joint are wedged into the openings of a set of links, such that a space is left between the back surface of the joint members and the walls of those openings.
U.S. Pat. No. 4,010,656 relates to a chain constructed of sets of interleaved links, each link having a pair of spaced, smooth walled, ovoid openings. The rocker joint comprises a pair of members each with a hypotrochoidal cross-sectional shape, i.e., they are generally three sided, each side having a convex surface. The members substantially match the shape of parts of the openings and engage those parts with a pair of its defining convex surfaces.
U.S. Pat. No. 4,507,106 teaches a rocker joint in which each pin or rocker of a pair has the identical cross-section, and in which each is defined by a front working surface of one radius and a back surface defined by second and third radii. Both of the radii defining the back surfaces are progressively smaller than the first radius, and an even smaller radius joins the front and back surfaces. The openings in the links are essentially round with smooth uninterrupted walls. While the rear surface matches a portion of the wall of the openings, the pins at times have a tendency to rotate relative to the opening which is not desirable.
When constructing a power transmission chain, it is common practice to make one of the pins of a rocker joint longer than the other. The shorter pin is trapped in position by the guide links which flank the sides of the chain while the longer pins are press-fitted or otherwise secured in the guide links. In other chains, the guide links are located centrally of the links. In any event, the guide links are used to maintain the engagement of the chain with the sprocket or sprockets with which the chain meshes and do not serve to transmit power to or from the sprockets.